Hi everyone I just thought about exploding batteries (who doesn´t XD). So my question : Can batteries (AA; AAA; LiPo; 9V, 6V Lantern, 4,5V; etc.) under some conditions like in the sun or if they are shorted or crushed... I was only interested in safety so I hope you can help me.

If you overheat a sealed battery then yes it can easy explode - a steam explosion. Most batteries have vents to prevent this as steam explosions are very violent. Some may be designed to split open at one end rather than explode - less dangerous but still nasty (electrolytic capacitors do this for instance).

LiPo's are a particular hazzard and can catch fire if abused - this is a lithium metal fire too, so water only fuels it. In general other batteries are safe if you don't overheat or over-current them.

All batteries are a chemically-based energy storage device and under the right, or should I say wrong, circumstances all types have the potential to destructivly release their energy, many in ways like combustion or ignition. However, the likelihood of this happening depends on many factors, the most important are energy density the chemicals used in the battery. As noted, LiPo batteries have a relatively high chance of type due to their high energy density and the fact they use lithium (which is a highly reactive element), so even realtively small LiPo batteries (i.e. even "button" type cells can experience ignition) can fail in rather spectacular and potentially dangerous ways. On the other end of the scale are alkaline batteries, which have very little chance of exploding in the way you probably mean it. However, they can rupture (sometimes significantly ripping through the battery) and/or leak if abused, which while not fun to watch still releases potassium hydroxide. A substance which can cause chemical burns in sufficient amounts.

Once, when I was a kid, I had an AA battery sitting on a bookshelf on it's side. I was laying in my bed, reading a book, when there was a loud !BANG! - it sounded like a small firecracker. I got up, and found the battery had shot the positive end (with I think the rod - which would make it a carbon-zinc cell, IIRC? I can't recall exactly...) off the battery across the room, where it hit the wall and bounced off of it; the body was still on the bookshelf.

LiPo batteries, though, are a known fire hazard - while charging, being exposed to heat, etc. In the R/C world, they sell special fireproof bags to charge LiPo batteries in. There's pics out there of people who've had fires because they overcharged their LiPo packs, or they charged them in a way in which the heat couldn't escape properly (this kind of thing caught a dorm room on fire at some school when the student was charging their laptop inside their laptop bag). Recently on Reddit there was a posting where a GPS device, mounted to the window (via suction cup mount) of what appeared to be an SUV, was left out in the sun, and the battery heated up, caught on fire, and ultimately burned up the interior of the car before it was put out. So you gotta be very, very extra careful around LiPo batteries.

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

nobody on this forum is going to agree with that. They are very safety conscious around here. In my personal experience I would say its unlikely but not something I would want to test. If you are worried about your setup causing a fire perhaps changing the setup would be in order?

When I worked for Racal Communications someone left a NiCd manpack radio battery connected to an ordinary lab DC power supply, there was a loud explosion and bits of battery were all over the place. Luckily, it happened at lunchtime and no-one was in the lab.

On field trials an officer was changing a manpack radio battery, with the radio upside down between his legs, and that battery exploded. He had to be treated for shock, but wasn't injured. The battery manufacturer eventually found that under certain conditions sparking occurred when the battery was changed, which could ignite hydrogen that was generated while it was charged. If the concentration was just right, there could be an explosion.

So lets say a normal AA battery can not burn my house down if it is shorted or exposed to heat (max. 45°C).

It would be rather unlikely. However if causes the wrong thing to catch fire, the smallest spark can cause a house to burn down just as much as any other ignition source. There some steps you should take anytime you want to use a battery in a custom design and be assured of safety:

First and most importantly, educate yourself on the battery type(s) you plan to use.

Second, think about the operating conditions (both the electrical and environmental conditions) you will be subjecting the battery to and if that poses any possibility of stressing the battery in a way that makes a fire or explosion more likely.

Third, if necessary modify your design in order to use the battery safely. This also includes changing the battery type to a non-recharable type, like common alkalines.

Forth, if for some reason it isn't feasible change your design to eliminate the possibility of fire or explosion; put the battery in a durable, non-flammable housing and isolate it as much as practical from flammable objects while providing as much ventilation as possible. Proper battery selection or modifying the circuit is always prefered to this last step, only go this route if there aren't any other realistic options.

Those are some general rules, more detail advice would depend upon the specifics of the application, operating conditions, and battery type involved.

Thanks for all your help. I know use non-recharable batteries and modified the project so that nofire hazard is possible. Thx.

So instead you will use resources that pollute landfills and you have to keep buying new batteries.

Ease off a bit on the guilt, I'm all for reducing the amount of trash a person sends to the land-fills but not at the expense of any one's home or driving them away from tinkering and DIY electronics projects. A person is more likely to do the other two "R"s (Reduce and Reuse) when building things for themself and not forced to only rely on commerically made products.

One thing I should clarify though to otzi, the most risk involved in with recharagable batteries is while recharaging them. So much of my warnings were for custom designs with one or more non-replacable recharagable batteries and a built-in recharging circuit (although you still don't want to expose any battery to temperature extremes, especially heat). So if your design uses standard sized alkalines; you should also be able to safely use a rechargable battery of the same size, provided you recharge them with a charager ment to be used on that size and type of battery.